Unknown,Transcriptomics,Genomics,Proteomics

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Expression data from Plasmodium falciparum schizonts

ABSTRACT: During intra-erythrocytic development, late asexually replicating Plasmodium falciparum parasites sequester from peripheral circulation. This facilitates chronic infection and is linked to severe disease and organ-specific pathology including cerebral and placental malaria. Immature gametocytes M-bM-^@M-^S sexual stage precursor cells M-bM-^@M-^S likewise disappear from circulation. Recent work has demonstrated that these sexual stage parasites are located in the hematopoietic system of the bone marrow before mature gametocytes are released into the blood stream to facilitate mosquito transmission. However, as sequestration occurs only in vivo and not during in vitro culture, the mechanisms by which it is regulated and enacted (particularly by the gametocyte stage) remain poorly understood. We generated the most comprehensive P. falciparum functional gene network to date by integrating global transcriptional data from a large set of asexual and sexual in vitro samples, patient-derived in vivo samples, and a new set of in vitro samples profiling sexual commitment. We defined more than 250 functional modules (clusters) of genes that are co-expressed primarily during the intra-erythrocytic parasite cycle, including 35 during sexual commitment and gametocyte development. Comparing the in vivo and in vitro datasets allowed us, for the first time, to map the time point of asexual parasite sequestration in patients to 22 hours post invasion, confirming previous in vitro observations on the dynamics of host cell modification and cytoadherence. Moreover, we were able to define the properties of gametocyte sequestration, demonstrating the presence of two circulating gametocyte populations: gametocyte rings between 0 and ~30 hours post invasion and mature gametocytes after around 7 days post invasion. We used 164/TdTom, a transgenic parasite line expressing a red fluorescent protein reporter under a gametocyte-specific promoter to generate schizont samples. Schizonts were subsequently isolated from both the fluorescent and non-fluorescent population by FACS and prepared for microarray analysis. Two biological replicates were produced for both the fluorescent and the non-fluorescent samples.

ORGANISM(S): Plasmodium falciparum

SUBMITTER: Matthias Marti

PROVIDER: E-GEOD-64887 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:For malaria transmission, the parasite must undergo sexual differentiation into mature gametocytes. However, the molecular basis for this critical transition in the parasites life cycle is unknown. Six previously uncharacterized genes, Pfg14.744, Pfg14.745, Pfg14.748, Pfg14.763, Pfg14.752 and Pfg6.6 that are members of a 36 gene Plasmodium falciparum-specific subtelomeric superfamily were found to be expressed in parasites that are committed to sexual development as suggested by co-expression of Pfs16 and Pfg27. Northern blots demonstrated that Pfg14.744 and Pfg14.748 were first expressed before the parasites differentiated into morphologically distinct gametocytes, transcription continued to increase until stage II gametocytes were formed and then rapidly decreased. Immunofluorescence assays indicated that both proteins were only produced in the subpopulation of ring stage parasites that are committed to gametocytogenesis and both localized to the parasitophorous vacuole (PV)b of the early ring stage parasites. As the parasites continued to develop Pfg14.748 remained within the parasitophorous vacuole, while Pfg14.744 was detected in the erythrocyte. The 5' flanking region of either gene alone was sufficient to drive early gametocyte specific expression of green fluorescent protein (GFP). In parasites transfected with a plasmid containing the Pfg14.748 5' flanking region immediately upstream of GFP, fluorescence was observed in a small number of schizonts the cycle before stage I gametocytes were observed. This expression pattern is consistent with commitment to sexual differentiation prior to merozoite release and erythrocyte invasion. Further investigation into the role of these genes in the transition from asexual to sexual differentiation could provide new strategies to block malaria transmission. Microarray analysis was used to compare two clones derived from Plasmodium falciparum strain 3D7 parasites that differ in their ability to undergo gametocytogenesis. Clone G+ produces gametocytes and clone G- produces very few if any gametocytes. RNA was harvested from the cultures when the asexual parasitemia was 0.9-1.48% (day 4) (n=4) after setting up the gametocyte cultures and 5.2-5.58% (day 6) (n=4) prior to the appearance of morphologically distinct gametocytes and used to generate cDNA that was labeled with Cy3 or Cy5 and hybridized to the Plasmodium falciparum 70 mer oligonucleotide microarray developed by DeRisi and co-workers.

Project description:The transmission of the malaria parasite between mosquitoes and mammals requires translational repression to ensure that only the proper proteins are expressed at the right time, while still allowing the parasite to prepare the mRNAs it will need for the next developmental stage. With relatively few known specific transcription factors (ApiAP2 family) that may specifically initiate gene transcription, Plasmodium parasites also regulate the stability and turnover of transcripts to provide more comprehensive gene regulation. The CAF1/CCR4/NOT complex has been shown in model organisms to be important for not only mRNA degradation, but also translational control through its deadenylases CAF1 and CCR4. However, few proteins that impose translational repression in Plasmodium sexual stages are known, and those that are characterized primarily affect female gametocytes. Therefore, we have characterized two deadenylases and have uncovered their roles in transmission. We have identified and characterized CCR4-1, which we show plays a role in activating male gametocytes, stabilizing transcripts in gametocytes, and regulating host-to-vector transmission. We find that when ccr4-1 is genetically deleted, there is a loss in the coordination of male gametocyte activation and a reduction in the ability of the parasite to productively infect the mosquito, which is independent of its effect upon male activation. Comparative RNA-seq shows that the deletion of ccr4-1 affects many transcripts that are translationally repressed in females, are related to male gamete function, and/or are important for early mosquito stage development. In contrast, we found that genetic deletion of the major deadenylase Caf1 is lethal. However, we observed that expression of only the N-terminal Caf1 domain is permissive, yet prevents proper complex assembly and phenocopies the ccr4-1 deletion. We therefore conclude that the general and transmission-specialized deadenylases of the CAF1/CCR4/NOT complex play critical and intertwined roles in parasite growth and transmission.

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Expression data from Plasmodium falciparum schizonts

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